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TYPES OF SEPARATOR
1. GAS / LIQUID SEPARATORS
A. The simplest type of Horizontal separator is shown in Figure : 10.
They are used to separate a two or three-phase inlet fluid into liquids and gas. The vessel inlet and gas outlet nozzles, consist of curved pipes which cause a change in direction of the inlet flow and the gas outlet. The liquid particles fall to the vessel bottom by gravity, while the gas rises to the top. This type of simple separator is not very efficient.
B. The 'Knock-Out Drum' is another simple type of separator as shown in Figure : 11.
It is used to separate a two or three phase inlet fluid into liquid(s) and gas.
The vessel inlet flow generally hits an inlet deflector plate to begin the separation process. Between the inlet and the gas outlet, some form of de-misting element may be installed which can be a wire mesh 'screen' or 'pad' or an angled vane type.
The demister construction presents a large surface area to the liquid mist entrained in the gas which causes small droplets of liquid to coalesce into larger drops which fall to the vessel bottom by gravity. The gas outlet nozzle exits the gas from the vessel above the demister screen
Figure : 10 - Separator
Figure : 11 -K.O. Drum
FACTORS AFFECTING SEPARATION
The following table shows some of the factors that affect separation :
|SEPARATION FACTOR ||EFFECT OF THE FACTOR
|1. Difference in Fluid Densities
||The greater the difference in densities, the easier the separation.
|2. Residence Time
||The longer the fluids are in the separator, the better the separation.
|3. Coalescing Element Surface Area
||The greater the area of the coalescing element, the better the separation.
Figure 12, is a field separator labelled as an actual operating unit together with control systems (The 'M's' are the inlet manifolds). After separation and metering, the oil and gas are re-combined and piped to the main production line feeding the plant GOSP facility. This operation saves the need for two pipelines - gas and oil - to the main facility where they will be separated along with other produced wells.
Figure: 12 -Typical, Single tube, 3-Phase Separator and Control System.
Figure 13, Shows a typical horizontal, Single tube, 3 - phase separator internal arrangement.
Figure 14, Shows a Double tube, 2 - phase separator internal arrangement.
Figure: 13 - Typical Horizontal, Single tube, Separator Internals
Figure: 14 - Double-tube Horizontal Separator
A: Fluid Inlet.
B: Primary Separation Section.
C: Secondary Separation Section.
D: Liquid Down-pipes to Lower Tube.
E: Gas Outlet.
F. Liquid Outlet
Figure : 15 -Typical Knock-Out Drum (3-Phase)
C. The Tangential or Cyclone Separator (Figures : 16 & 17).
This type operates by centrifugal force. It is used to separate a two or three phase inlet fluid into liquid(s) and gas. The inlet flow enters the vessel side at a tangent to the circumference.
This causes the fluids to rotate at high speed inside the drum. The centrifugal force of rotation causes the heavier liquid particles to be forced downwards while the lighter gases are forced upwards.
Again, a demister screen may be installed near the vessel top to coalesce liquid droplets from the gas and drop them back into the liquid.
Some de-misters consist of 'Packing' type materials like 'Raschig Rings', 'Ceramic Saddles' or other suitable materials. As seen in Figure: 17
Note: Demister screens can become fouled and lose efficiency. From time to time, it is necessary to shut down the separator and remove the demister for cleaning or renewal.
Figure 16: Tangential or Cyclone Separator
Figure 17: Two-Phase Cyclone Separator
The two magnified drawings indicate 2 types of demister systems that may be used in separators.
A. Represents 'Conical Impingement' contacting devices.
B. Shows a packed bed of loose 'Raschig Rings'.
Each type coalesces the droplets of mist entrained in the gas and, as they form larger droplets, they fall into the bottom liquid. (Droplet size is exaggerated)